Novel surface plasmon waveguide for high
integration

Liu Liu, Zhanghua Han, and Sailing He

Liu Liu,a,b Zhanghua Han,a and Sailing Hea,c

aCentre for Optical and Electromagnetic research, Zhejiang University, Joint Research Center of Photonics of the
Royal Institute of Technology (Sweden) and Zhejiang University, Yu-Quan, Hangzhou, 310027, China

Abstract

A novel surface plasmon waveguide structure is proposed for highly integrated planar lightwave circuits. By etching a small trench through a metallic thin film on a silica substrate, a guided mode with highly confined light fields is realized. The mode properties of the proposed structure are studied. The necessity of using a polymer upper-cladding is discussed. The coupling between two closely positioned waveguides and a 90° bending are also studied numerically. Sharp bending and high integration can be realized with the present surface plasmon waveguide. The proposed structure is easy to fabricate as compared with some other types of surface plasmon waveguides for high integration.

Real part βr of the propagation constant for different modes when w=50nm. The insets show some typical mode profiles of Ex for the corresponding modes. The dot-dashed line indicates the real part βsp of the propagation constant for the SP wave supported by the metal film without the trench.

Dependence of the mode properties on the structural parameters in the proposed SP waveguide. The two black solid lines indicate the boundaries of different regions. The colored curves give the contours of the propagation length (indicated with numbers) for the fundamental mode.

Real part βr of the propagation constant for the fundamental mode as the refractive index of the cladding decreases when h=400nm. The dot-dashed line indicates the real part βsp of the propagation constant for the SP wave supported by the metal film without the trench.

(a) Two closely positioned SP waveguides. (b) The dependence of the coupling length on separation D when w=50nm and h=200nm. (c) The dependence of the coupling length on the metal film thicknesses h and the trench width w when D=150nm.

(a) Schematic diagram of a 90° bending (top-viewing x-z plane). The amplitude distribution of Hy field in the x-z plane at the central depth of the metal films when the bending radius (b) r=0nm and (c) r=100nm. (d) The transimissivity, reflectivity and out-of-plane loss as the bending radius r increases. The transimissivity (reflectivity) is evaluated as the power propagating (reflected) through the output (input) facet of the bending section. The out-of-plane loss is evaluated as the power radiated out of the bending plane (the x-z plane). All these powers are normalized by the input power at the input facet of the bending section.